FIG. 1 shows a circuit diagram of a boost type converter in the prior art. In the configuration of boost type converter of FIG. 1, it includes a rectifier bridge (bridge) having four unidirectional switches (e.g., four diodes), a first output terminal and a second output terminal, and a boost converter (or a boost PFC). The rectifier bridge receives an AC input voltage Vin, and the boost converter includes a power switch S having a first and a second terminals, an inductor L having a first and a second terminals, a unidirectional switch D having first terminal and a second terminal (e.g., a diode having an anode and a cathode), and an output capacitor C having a first and a second terminals and outputting a DC voltage Vo. The first terminal of the power switch S is coupled to the second terminal of the inductor L and the first terminal of the unidirectional switch D, the second terminal of the power switch S is coupled to the second output terminal of the rectifier bridge and the second terminal of the output capacitor C, the first terminal of the inductor L is coupled to the first output terminal of the rectifier bridge, and the first terminal of the output capacitor C is coupled to the second terminal of the unidirectional switch D. The AC input voltage Vin stores an energy in the inductor L when the power switch S is turned on, the AC input voltage Vin provides the output power and the energy stored in the inductor L is also transmitted to the load when the power switch S is turned off.
FIG. 2 shows a circuit diagram of a buck type converter in the prior art. In the configuration of buck type converter of FIG. 2, it includes a rectifier bridge (bridge) having four unidirectional switches (e.g., four diodes), a first output terminal and a second output terminal, and a buck converter (or a buck PFC). The rectifier bridge also receives an AC input voltage Vin, and the buck converter includes a power switch S having a first and a second terminals, an inductor L having a first and a second terminals, a unidirectional switch D having a first terminal and a second terminal (e.g., a diode having an anode and a cathode), and an output capacitor C having a first and a second terminals and outputting a DC voltage Vo too. But, the connection relationships in FIG. 2 are different from those of the boost converter in FIG. 1. In FIG. 2, the first terminal of the power switch S is coupled to the first output terminal of the rectifier bridge, the second terminal of the power switch S is coupled to the first terminal of the inductor L and the second terminal of the unidirectional switch D, the first terminal of the unidirectional switch D is coupled to the second output terminal of the rectifier bridge and the second terminal of the output capacitor C, and the second terminal of the inductor L is coupled to the first terminal of the output capacitor C. The AC input voltage Vin provides the output power and stores an energy in the inductor L when the power switch S is turned on, and the energy stored in the inductor L is transmitted to the load when the power switch S is turned off.
FIG. 3 shows a circuit diagram of a buck/boost type converter in the prior art. In the configuration of buck/boost type converter of FIG. 3, it includes a rectifier bridge (bridge) having four unidirectional switches (e.g., four diodes), a first output terminal and a second output terminal, and a buck/boost converter (or a buck/boost PFC). The rectifier bridge also receives an AC input voltage Vin, and the buck/boost converter includes a first and a second power switches S1 and S2, each of which has a first and a second terminals, an inductor L having a first and a second terminals, a first and a second unidirectional switches D1 and D2, each of which has a first terminal and a second terminal (e.g., two diodes, each of which has an anode and a cathode), and an output capacitor C having a first and a second terminals and outputting a DC voltage Vo too. The first terminal of the first power switch S1 is coupled to the first output terminal of the rectifier bridge, the second terminal of the first power switch S1 is coupled to the first terminal of the inductor L and the second terminal of the first unidirectional switch D1, the first terminal of the first unidirectional switch D1 is coupled to the second output terminal of the rectifier bridge, the second terminal of the second power switch S2, and the second terminal of the output capacitor C, the second terminal of the inductor L is coupled to the first terminal of the second unidirectional switch D2 and the first terminal of the second power switch S2, and the second terminal of the second unidirectional switch D2 is coupled to the first terminal of the output capacitor C. The buck/boost converter can be viewed as the aforementioned buck and boost converters connected in series. The buck/boost converter operates in the buck mode, the power switch S2 is continuously turned off, and the unidirectional switch D2 is continuously turned on when the input voltage Vin (after its rectification) is larger than the output voltage Vo. The buck/boost converter operates in the boost mode, the power switch S1 is continuously turned on, and the unidirectional switch D1 is continuously turned off when the input voltage Vin (after its rectification) is less than the output voltage Vo.
The buck type and buck/boost type converters can be set such that the output voltage Vo is smaller than the input voltage Vin (after its rectification). Due to that input voltage Vin (after its rectification) is approximated to the output voltage Vo, the efficiency of the converter can be raised effectively when the input voltage is low. Besides, the design flexibility of the DC/DC converters is increased following the decrease of the output voltage Vo.
But, the buck type and buck/boost type converters also have their drawbacks described as follows.
1. Due to the control of the turn-on and the turn-off of the respective power switch S (S1) of the buck type and buck/boost type converter, a quite large impulse energy is released to the two terminals of the power switch S (S1) once the power switch S (S1) is turned off, and a very high peak switch current is generated and might cause the damage of the power switch when the AC input voltage exceeds an overvoltage threshold.
2. Usually, the buck type and buck/boost type converter is not operated to decrease the standby power consumption of the power source and the power switch S (S1) is turned off when the power source of desk-top computer/server is operated under a standby mode. If the standby power source is connected after the buck type and buck/boost type converter, then it can not be operated normally at this time. If the standby power source is connected after the rectifier bridge, then the standby power source can not maintained a normal output voltage for a predetermined time.
To solve the above-mentioned problem, configurations employed the buck type and buck/boost type converters are proposed in the present invention.
Keeping the drawbacks of the prior arts in mind, and employing experiments and research full-heartily and persistently, the applicants finally conceived buck and, buck/boost converter systems having auxiliary circuits and method thereof.